Trace your hoses it should be in the center of the firewall way up under the wireing harness there is a steel line with the port right in the middle.
The 1991 VW Jetta low pressure port can be found on the air conditioning compressor. There are two ports, the low pressure port will be labeled as such.
under the battery
On a 1991 Mazda Miata, the freon port for the air conditioning system is located on the passenger side of the engine bay. You'll find the low-pressure service port near the firewall, typically covered with a plastic cap. The high-pressure port is located near the front of the engine bay, close to the condenser. Always ensure the engine is off and the system is depressurized before attempting to access the ports.
Larger hose from the air compressor
The air conditioning relay on a 1991 Mitsubishi Lancer is typically located in the engine compartment, near the fuse box. It may be mounted on the driver's side fender or near the battery. Consult the vehicle's service manual for the exact location and diagram to assist in locating it.
The oil pressure sensor is located behind the engine just to the right of the coil packs
The low pressure cap is in the front of the engine compartment. Stand facing the engine and to the left just behind the radiator U will see an air conditioning line. There will be a black cap that should have an L on it but it might be worn off. That is your low pressure cap.
In a 1991 3.3l the oil pressure switch is located beside the oil filter
In the throttle body.
To recharge the air conditioning on a 1991 Jeep Cherokee, first locate the low-pressure service port, typically found on the larger diameter A/C line. Attach a refrigerant can with a gauge to this port, ensuring the can is held upright. Start the engine and turn the A/C to maximum; then, slowly release the refrigerant into the system while monitoring the gauge. Be cautious not to overcharge, and check for any leaks or issues after recharging.
Follow the rail line that runs to the injectors. You will find the pressure regulator.
The 1991 Acura Legend does not have an oil temperature sensor. It does have an oil pressure sensor. The oil pressure sensor will be located on the left-hand side of the engine.